Mobile geolocation

ABSTRACT

A method and apparatus for generating reference signatures for use in geolocation in a cellular wireless communication system is provided. A first signature for a mobile communication unit comprises location information, a timestamp, and radio frequency measurement information obtained by a mobile communication unit at a location, but does not contain identification information for the mobile communication unit. The first signature is compared to signatures in a database, to identify a second signature that has a timestamp and radio frequency measurement information that correspond to those of the first signature. A reference signature is created by combining at least a part of the first signature with at least a part of the second signature. Repetition of the comparison and combination steps creates a database of reference signatures, for use in geolocating other received call signatures.

CROSS REFERENCE TO RELATED U.S. APPLICATIONS

This application is related to copending U.S. patent application Ser.No. ______, entitled METHOD AND SYSTEM FOR MOBILE REFERENCE SIGNATUREGENERATION and having atty docket no. Arieso-24055 and also toco-pending U.S. patent application Ser. No. ______, entitled MOBILECOMMUNICATION SYSTEM and having atty docket no. Arieso-24060, both filedDec. 18, 2012, and the disclosures of which are both incorporated hereinby reference.

FIELD OF THE INVENTION

The field of the invention relates to a system and method for generatingreference signatures in a mobile communication system.

BACKGROUND OF THE INVENTION

Wireless communication systems, such as GSM and the 3^(rd) Generation(3G) of mobile telephone standards and technology, are well known. Anexample of 3G standards and technology is the Universal MobileTelecommunications System (UMTS™), developed by the 3^(rd) GenerationPartnership Project (3GPP™) (www.3gpp.org).

The 3^(rd) and 4^(th) generations of wireless communications, and inparticular systems such as LTE, have generally been developed to supportmacro-cell mobile phone communications. Here the ‘phone’ may be a smartphone, or another mobile or portable communication unit that is linkedwirelessly to a network through which calls are connected. Henceforthall these devices will be referred to as mobile communication units.‘Calls’ may be data, video, or voice calls, or a combination of these.An increasing proportion of communications involve data rather thanvoice, and are technically referred to as being a ‘connection’, ratherthan a ‘call’.

Macro cells utilize high power base stations to communicate withwireless communication units within a relatively large geographicalcoverage area. The coverage area may be several square kilometers, orlarger if it is not in a built-up area.

Typically, mobile communication units communicate with each other andother telephone systems through a network. In a 3G system, this is the‘Core Network’ of the 3G wireless communication system, and thecommunication is via a Radio Network Subsystem. A wireless communicationsystem typically comprises a plurality of Radio Network Subsystems. EachRadio Network Subsystem comprises one or more cells, to which mobilecommunication units may attach, and thereby connect to the network. Abase station may serve a cell with multiple antennas, each of whichserves one sector of the cell. Often a cellular wireless communicationsystem is described as comprising two parts: the network; and the mobilecommunication units.

FIG. 1 provides a perspective view of one prior art wirelesscommunication system 100. The system of FIG. 1 comprises a network ofbase stations, comprising BS1 with reference 110, BS2 with reference120, BS3 with reference 130, BS4 with reference 140 and BS5 withreference 150. Only one mobile communication unit 105 is shown. In areal network, there may be anywhere from thousands to millions of mobilecommunication units.

A base station such as base station 110 communicates with mobilecommunication unit 105. Base station 110 allows mobile communicationunit 105 to place calls through the network, and receive calls routedthrough the network to base station 110.

Base station 140 has been shown as having a coverage area 142. If basestation 140 had an omnidirectional antenna, and the terrain were flat,then coverage area 142 might be circular. However, both the shape andextent of the coverage areas of a typical base station depend on manyvariables, and may change with time.

Controller 160 manages calls within the wireless communication system100. Controller 160 would be linked to all the base stations BS1-BS5,but the links are not shown in order to keep FIG. 1 simple to interpret.Controller 160 may process and store call information from the basestations shown in FIG. 1, plus many other base stations not shown inFIG. 1. In a UMTS network, controller 160 may be linked to the basestations via one or more Radio Network Subsystems.

There may be significant advantage in knowing where in wirelesscommunication system 100 a mobile communication unit 105 is located.Prior art wireless communication systems have provided a variety ofsolutions to the problem of ‘geolocating’ mobile communication unit 105.One known solution involves providing specific equipment within themobile communication unit that can measure location, such as a GPS unit.However, many users switch off the GPS function on their mobilecommunication units. Partly as a consequence, reported GPS details arehighly infrequent. As little as one call in ten-thousand connectionsmight report a GPS coordinate.

One prior art solution indicates that absolute power transmission levelscan be used to geo-locate the mobile station. See for example “MobileCellular Location Positioning: An Approach Combining Radio SignalStrength Propagation and Trilateration”, M. F. Khan, Masters Thesis,University of Johannesburg, November 2009 which is herein incorporatedby reference in its entirety. However, power measurements inevent-driven technologies, such as LTE, can be relatively infrequent.Even where a system or mobile communication unit has the capability ofperforming geolocation based on absolute power measurement, it mayremain very important to make use of whatever alternate sources ofinformation are also available.

Co-pending U.S. patent application Ser. No. 13/311,132, with applicantreference OPT004P326, which is herein incorporated by reference in itsentirety, indicates that differential power levels can be used togeo-locate a mobile unit. A mobile communication unit provides ameasurement of the difference in signal strengths that it receives fromat least two base stations. The difference value can be compared to oneor more contours of constant power difference, for signals received bysubscriber mobile communication units in the system. An estimate oflocation can be obtained from this comparison. However, differentialpower techniques can be limited in scenarios where there are few pilotsignals to make use of.

Patent application WO2010/083943A, which is also incorporated byreference in its entirety, shows a further technique, which uses signalstrength and timing data derived from the mobile communication unititself, along with network configuration data provided by the networkoperator, to locate the mobile communication unit.

Co-pending U.S. patent application Ser. No. 13/369,591, with applicantreference OPT004P330, and is hereby incorporated by reference in itsentirety indicates that a database of ‘known’ signatures can be used toaid in locating a mobile communication unit operating in a mobilecommunication system. Each known signature comprises a locationmeasurement or estimate, together with radio frequency and othermeasurements that were obtained by a mobile communication unit at thatlocation at a particular time. Examples of the ‘other measurements’ thatmay be obtained by a mobile communication unit are: control information;a set of cells observable by the first mobile communication unit; andreceived power level information, for signals received from theobservable cells.

The use of this database of known signatures enables position estimatesto be derived, at least for any mobile communication devices that reportsimilar values of the radio frequency and other measurements to those ofa known signature. When a ‘match’ of such similar values is found, themobile communication device concerned can therefore be assumed to be atthe location at which the known signature was recorded.

U.S. patent application Ser. No. 13/369,591 also employs ‘contextinformation’. Context information links successive known signatures inthe database. When two or more signatures are received from a mobilecommunication device whose location is unknown, those signatures can becorrelated against two or more signatures in the database that arelinked by context information.

The invention of U.S. patent application Ser. No. 13/369,591 only allowsthe estimation of the position of a mobile communication device if thereis a match between a known signature in the database and the values ofthe radio frequency and other measurements reported by that mobilecommunication device. This approach therefore relies on the databasehaving many known signatures. For a cellular two-way radio system, thedatabase may require hundreds of thousands or millions of knownsignatures. Obtaining these known signatures may be difficult. Oneapproach is to collect signatures having location information byemploying ‘drive testing’ and/or ‘indoor-walk-testing’. Such testingrelies on moving a test mobile communications device through a network,in order to collect accurate position measurements from the mobilecommunication device and at the same time measure, for those positions,the values of radio frequency and other measurements.

Drive-testing and indoor-walk-testing have the disadvantages that:

(i) Drive- and walk-test signatures may not be easily obtained in theareas most frequented by actual users. This is because some areas arenot accessible for either drive- or walk-testing, such as privatecompany premises.

(ii) Signatures can be expensive to obtain over extensive areas.

Signatures obtained from drive- or walk-testing can be augmented byselecting data from the Operation Support System (OSS) of the mobilecommunication system. The OSS holds measurements made by many or all ofthe subscriber mobile communication units that operate in a mobilecommunication system. Some or all of the calls made during drive- orwalk-testing will result in a record being created in the OSS. In somesystems, the record of the call from the test mobile communicationsdevice and the corresponding record from the OSS both containidentification information for the test mobile communications device. Ifthis is the case, then the common identification information can beused. If the correct individual record can be retrieved from the OSS bymatching its identification information with the identificationinformation for the test mobile communications device used in the driveor walk testing, then the records can be combined. In particular, therecord retrieved from the OSS may contain measurements made by themobile communication system that can be added to the record of the samecall that was made by the test mobile communications device itself aspart of drive or walk testing.

Thus the identification information in both records allows the tworecords to be identified as being from the same mobile communicationdevice. This may in turn then allow the two records to be synthesizedinto a more comprehensive signature than was obtained directly from thetest mobile communications device.

Cellular wireless communication systems have faced the disadvantagesthat signatures may be expensive to obtain by known methods, and may notbe representative of the areas where users make calls. Hence, there is aneed for an improved method for generating reference signatures in amobile communication system, such as an LTE, GSM or UMTS network.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying figures, where like reference numerals refer toidentical or functionally similar elements throughout the separate viewsand which together with the detailed description below are incorporatedin and form part of the specification, serve to further illustratevarious embodiments and to explain various principles and advantages allin accordance with the present invention.

FIG. 1 is a schematic diagram, illustrating a prior art cellularwireless communication system.

FIG. 2 is a schematic diagram, illustrating two databases for a cellularwireless communication system.

FIG. 3 provides more detail of the signatures in the first and seconddatabases of FIG. 2.

FIG. 4 illustrates links that may be created between correspondingsignatures in the databases of FIG. 2.

FIG. 5 illustrates the creation of a database of reference signatures.

FIG. 6 illustrates locations at which signatures are recorded in amobile communication system of an embodiment.

FIG. 7 illustrates a further embodiment of a database of referencesignatures.

FIG. 8 is a flowchart of a method of creating and using a database ofreference signatures.

Skilled artisans will appreciate that elements in the figures areillustrated for simplicity and clarity and have not necessarily beendrawn to scale. For example, the dimensions of some of the elements inthe figures may be exaggerated relative to other elements to help toimprove under-standing of embodiments of the present invention.

DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS

Before describing in detail embodiments that are in accordance with thepresent invention, it should be observed that the embodiments resideprimarily in combinations of method steps and apparatus componentsrelated to a computer camera lighting system and method. Accordingly,the apparatus components and method steps have been represented whereappropriate by conventional symbols in the drawings, showing only thosespecific details that are pertinent to understanding the embodiments ofthe present invention so as not to obscure the disclosure with detailsthat will be readily apparent to those of ordinary skill in the arthaving the benefit of the description herein.

In this document, relational terms such as first and second, top andbottom, and the like may be used solely to distinguish one entity oraction from another entity or action without necessarily requiring orimplying any actual such relationship or order between such entities oractions. The terms “comprises,” “compromising,” or any other variationthereof, are intended to cover a non-exclusive inclusion, such that aprocess, method, article, or apparatus that comprises a list of elementsdoes not include only those elements but may include other elements notexpressly listed or inherent to such process, method, article, orapparatus. An element proceeded by “comprises . . . a” does not, withoutmore constraints preclude the existence of additional identical elementsin the process, method, article or apparatus that comprises the element.

A cellular wireless communication system and a method of generatingreference signatures for use in geolocation in a cellular wirelesscommunication system are provided. The cellular wireless communicationsystem may, for example, operate in accordance with the GSM, UMTS or LTEstandards.

A method of generating reference signatures for use in geolocation in acellular wireless communication system comprises obtaining a firstsignature for a mobile communication unit, the first signaturecomprising location information, a timestamp and radio frequencymeasurements obtained by the mobile communication unit at the location,but not containing identification information for the mobilecommunication unit. The first signature is compared to signatures in adatabase, to identify a second signature of the plurality of signatures,the second signature having a timestamp and radio frequency measurementinformation that correspond to those of the first signature. Based onthis comparison, a first reference signature is created by combining atleast a part of the first signature with at least a part of the secondsignature. Creating the first reference signature may further comprisecombining the location information of the first signature with at leasta part of the second signature.

The location information of the first signature may be added into thedatabase holding the second signature. The database holding the secondsignature may be the OSS database of a UMTS network. As a result ofadding in the location information of the first signature, a referencesignature may be created that has:

(i) location information;

(ii) a timestamp;

(iii) radio frequency measurements of the type available with the secondsignature;

(iv) radio frequency measurements of the type available with the firstsignature, if these are added to the database together with the locationinformation of the first signature.

Repetition of the comparison and combination steps for many ‘firstsignatures’ creates a database of reference signatures. Those referencesignatures may then be used to provide geolocation estimates for otherreceived call signatures. By repeating the method of the invention,therefore, it is possible to enrich the signatures in the database. Theresulting set of reference signatures in the database is then availablefor matching to a variety of other signatures, which do not contain alocation measurement from the mobile communication unit that created thesignature. These signatures may be received, after creation of theenriched database of signals, from mobile communication units whosecurrent location is unknown but needed.

The second signature may comprise a user identifier, and at least one ofthe following types of control information not included in the firstsignature: timing advance; burst throughput rate; dynamic rate controlcomprising at least channel quality indicators; signal-to-noise ratio.

The first signature will typically have some radio frequencymeasurements. However, these measurements may cover fewer variables thanare usually available for signatures in the OSS database of a UMTSnetwork. The radio frequency measurements comprised in the firstsignature may comprise at least one selected from: signal quality; acell identifier and corresponding observed power level. There may bemore than one observed power level available, each for a correspondingcell.

A variety of sources may provide the first signature. However, the firstsignature may be taken from an anonymized call database. Such a databasemay contain large numbers of signatures, each with a location estimate.However, the signatures in the anonymized call database have beenrecorded without any identification of either the user or the mobilecommunication unit that made the call to which the signature relates. Anexample of an anonymized call database is a database compiled inaccordance with the Minimization of Drive Test 3GPP standard. The 3GPPMinimisation of Drive Test standard is explained in standards documents3GPP TS 37.320 and TS 32.422.

Anonymized call databases have hitherto been only of limited use. Suchanonymised databases are ‘rich’ in location information about where amobile communication unit was located when it made a call. However, theycan be considered to be limited databases in the sense that theytypically both:

(i) Lack user identity information; and

(ii) Provide only a relatively small amount of data, such as informationonly about received powers and serving cells.

The present invention links a ‘first’ signature from such an anonymisedcall database with another record of the same call by the same mobilecommunication unit, the other record being the second signature referredto above. Although the first signature has no identificationinformation, it has sufficient information to enable the correspondingsecond signature to be identified as a ‘match’. The second signature isin effect being identified and selected from among very many potentialcandidates in the database.

For example, the first signature may comprise a timestamp and a cellidentifier. The precision of the timestamp recording (typically inmilliseconds) and the uniqueness of the reported cells (typically usingglobal cell identifiers) permit a matching between the first and secondsignatures. If, in another example, the first signature comprises atimestamp and an observed power level, then the precision of thetimestamp and the precision of the RF measurement (typically in deciBelsrelative to a milliwatt, or dBm) also permit a matching between thefirst and second signatures.

At any given time in a large mobile communication system, a cell mayserve hundreds, thousands or even tens of thousands of mobilecommunication units. In order to allow unique identification of recordsin such systems, the invention may comprise, for each of those cells,matching: (i) the timestamps of first and second signatures; (ii)information about multiple cells that could be observed; and (iii)either signal strengths or signal quality.

The type of information contained in a location-rich, information-poordatabase is often infrequently available, so the anonymised database isrelatively sparsely populated. For example, there may only be entriesfor calls that occurred under certain RF-related handoff triggerconditions. The entries in the location-rich, information-pooranonymised database are created generally much less often than non-RFcontrol data would be provided for calls. So only a subset of all callswill result in a signature being created in the anonymised database. Incontrast to this, databases such as the OSS database of a UMTS systemcan be considered to be ‘information-rich, but location poor’, at leastrelative to the anonymised database. The OSS database may capturemeasurement and control events for every call. So, typically, entriesare created in the OSS database much more often than entries in theanonymised database.

When the method of the invention is repeated, it may be possible tocreate a link between many, or possibly all, entries in the anonymiseddatabase and the corresponding signatures for the same calls in the‘information-rich, but location poor’ database. Effectively, the twodatabases are being combined, to provide many new reference signatures.In one embodiment, the database of ‘second’ signatures can be augmented,by the addition of location information for each second signature, forwhich it has been possible to create a link to the corresponding firstsignature. This approach allows the construction of inexpensive, complexreference signatures through the linking of information in location-richand information-rich databases. Those reference signatures can then beused for geolocation of other calls.

FIG. 2 provides an exemplary illustration of two databases. In thisexample, first database 210 comprises signatures 212, 214, 216, 218,220. First database 210 may, for example, be the OSS database of a UMTScommunications system. In a real UMTS communications system, firstdatabase 210 may comprise millions of entries, for even a 24 hour periodin which calls or data connections are made in the mobile communicationsnetwork.

The identification field is the first part of each signature in firstdatabase 210. The identification field may, for example, comprise theInternational Mobile Subscriber Identity (IMSI) number of the mobilecommunication unit concerned. Each of signatures 212, 214, 216, 218represents information from the same mobile communication unit SU1, butat successively later time points. For each of signatures 212, 214, 216,218, the identification field contains the same entry SU1, as eachsignature is for the same mobile communication unit SU1.

Each of signatures 212, 214, 216, 218 also comprises one or more furtherfields. Signatures 212 and 218 each include a second field, whichcontains RF measurements. Signature 212 has RF measurement RF1, andsignature 218 has RF measurement RF3. Those measurements may typicallyinclude many of the following: timing advance; burst throughput rate;data throughput rate; dynamic rate control, comprising at least channelquality indicators; signal-to-noise ratio; a timestamp; a cellidentifier; and an observed power level. Signature 218 might typicallyhave been obtained somewhere in the range of 1-100 seconds aftersignature 212.

Signatures 214 and 216 were obtained after signature 212 but beforesignature 218. Each of signatures 214 and 216 includes a second field,which contains control information. Signature 214 has controlinformation denoted as ‘Control 1’. Signature 216 has controlinformation denoted as ‘Control 2’. However, signatures 214 and 216 donot include the detailed RF measurements that are included in signatures212 and 218. Each of signatures 214 and 216 includes a timestamp.

Signature 220 is an example of one signature for a different mobilecommunication unit, SU2. So signature 220 has entry SU2 in itsidentification field. Signature 220 also includes RF measurement RF4.Signature 220 will not be considered in detail in relation to FIG. 2,and is provided to illustrate that the first database 210 has signaturesfor various different mobile communication units.

Mobile communication unit SU1, when in communication with the cellularnetwork, will report various RF and control data in the life of a dataconnection or voice call. It is these report parameters that lead to thesignatures 212, 214, 216, 218, which may all arise during one singlecall/connection involving SU1. Similarly, mobile communication unit SU2will report various RF and control data in the life of one of its dataconnections or voice calls, which results in signature 220 and possiblyseveral or many others, not shown. In a UMTS network, all of thesignatures with RF and control data are placed in an Operations SupportSystem (OSS) database, along with the user identity and timestampdetails. So first database 210 may simply be the OSS database of acellular network, or may alternatively be a dedicated/bespoke database.

Second database 230 is a location rich database, which is relativelypoor in the information that it holds. Each signature in second database230 does contain a location measurement. Each signature in seconddatabase 230 may contain a different and/or more limited set of RFmeasurements, than the RF measurements that form part of signatures 212,218 and 220 in first database 210. Also, each signature in seconddatabase 230 does not contain information about the identity of themobile communication unit that made the call, so second database 230 isan anonymised database.

Mobile communication unit SU1 may make many data connections and voicecalls, each giving rise to a different set of signatures such as 212,214, 216, 218 in first database 210. For one or more of these calls,mobile communication unit SU1 may also provide a report that is includedin a second database 230. In the example shown in FIG. 2, there arethree signatures in second database 230. Signatures 232 and 236 haveboth been recorded for mobile communication unit SU1. Signature 232 wasrecorded before signature 236. Both signatures 232 and 236 comprise alocation estimate for mobile communication unit SU1.

Signature 232 contains location estimate LOC1, and RF information RF1A.Signature 232 is a record of measurements of the same call by mobilecommunication unit SU1 as signature 212 in first database 210, with bothsignatures 232 and 212 being made at the same timepoint. Thus at leastsome parts of the RF information RF1A contained in signature 232 willcorrespond closely to at least some parts of RF information RF1 insignature 212.

Signature 236 contains location estimate LOC3, and RF information RF3A.Signature 236 is a record of measurements for the same call by mobilecommunication unit SU1 as signature 218 in first database 210, with bothsignatures 236 and 218 being made at the same timepoint. Thus at leastsome parts of the RF information RF3A contained in signature 236 willcorrespond closely to at least some parts of information RF3 insignature 218.

A signature 234 is also recorded in second database 230, but relates toa third mobile communication unit SU3. Signature 234 was recorded aftersignature 232, but before signature 236. Signature 234 is included inthis example only to show that second database 230 contains othersignatures, from other mobile communication units than mobilecommunication unit SU1. Signature 234 contains location estimate LOC2and RF information RF2A. Somewhere in first database 210 there may beone or more signatures, which are not shown on FIG. 2, which can belinked to signature 234.

Signatures 232, 234 and 236 in second database 230 may be recorded if,for example, mobile communication units are selected to contributeanonymously to a limited RF database. The limited RF database might be a‘Minimisation of Drive Test’ database. The selection of the mobilecommunication unit and call or data connection might be done at random.The resulting signature recorded in second database 230 may comprise:

(i) location information, such as a location coordinate, which might besupplied by GPS;

(ii) some limited RF information, such as power levels and observedcells;

(iii) a timestamp.

Only when mobile communication unit SU1 is actively engaged incollecting ‘Minimization of Drive Test’ data, therefore, would itroutinely provide location information such as that in signatures 232and 236. Otherwise, when not engaged in collecting Minimization of DriveTest data, mobile communication units such as mobile communication unitSU1 might typically provide location information for only one out ofevery ten-thousand calls or data connections.

Known approaches, such as that in copending application Ser. No.13/369,591, could be applied just to the entries in a location rich,information poor database such as second database 230. However:

(i) Those entries may only include limited RF parameters. The parametersmight be just observed cells and observed power levels.

(ii) There would be relatively few entries. A location rich, informationpoor database is infrequently populated, because generation of these RFmeasurement reports is triggered by relatively infrequent call events orRF conditions.

(iii) The entries would not contain more-frequently-available non-RFcontrol information, such as CQI, burst rate, etc.

(iv) The context of each RF measurement would be lost, due to theanonymous recording that is employed. The “context” is defined aspreservation of temporal order of signatures and association with thesame mobile communication unit. This is explained in greater detail incopending U.S. application Ser. No. 13/369,591.

Known approaches do not make a link between signatures in location poor,information rich databases such as first database 210, and locationrich, information poor databases, such as second database 230.

The invention utilizes the fact that a location poor, information richdatabase, such as first database 210 or an OSS database, would containall of the RF parameters that were sent to the limited RF database andmuch more. The extra information in first database 210, such as useridentity and non-RF control information, is not typically stored withlocation information, but the invention may enable retrieval of therelevant location information from the location rich, information poordatabases, such as second database 230.

FIG. 3 provides more detail of signature 212 from first database 210,and signature 232 from second database 230. These are represented inFIG. 3 as signature 312 and signature 332, respectively.

Signature 312 from first database 310 has been illustrated as comprisingmultiple measurements. Each of these measurements has suffix 1, toconform to the suffix RF1 used in FIG. 2 for signature 212. Signature332 from second database 330 has been illustrated as comprising multiplemeasurements. Each of these measurements has suffix 1A, to conform tothe suffix RF1A used in FIG. 2 for signature 232.

Signature 312, in this example, comprises: Cell identifier 1, reference316; Timestamp 1, reference 318; Signal-to-noise ratio 1, reference 320;Channel quality indicator 1, reference 322; Dynamic rate control 1,reference 324; Burst throughput rate control 1, reference 326; Timingadvance 1, reference 328. Signal to noise ratio and channel qualityindicator are examples of quantities used in ‘dynamic rate control’.However, the dynamic rate control shown by reference 324 may be based onother parameters than signal to noise ratio and channel qualityindicator.

Signature 332, in this example, comprises: Location information LOC1,reference 334; Power level 1A, reference 336, Observed cells 1A,reference 338; Timestamp 1A, reference 340.

When a mobile communication unit provides measurements, it willtypically be able to see more than one cell. So, typically, there willbe a power level associated with each observed cell. Signature 312 willtherefore comprise further measurements corresponding to those shown asreferences 320-328, but for a second cell and other cells. Thoseadditional measurements are not shown on FIG. 3. Similarly, signature332 will comprise additional measurements corresponding to the powerlevel measurement in reference 336, but for the second and other cells.FIG. 3 has only been drawn to illustrate measurements for a first cell.

Signature 312 and signature 332 may be linked by using the overlappingtimestamp and RF measurements held in the two signatures. The timestamprecording is precise, and may typically be recorded in milliseconds. Theprecision of the RF measurement recordings is also high, with recordingstypically in deciBels relative to a milliwatt, or dBm. In addition, theuniqueness of the reported cells may be used, with the cells typicallybeing identified using global cell identifiers. When such links can beestablished, there is a very high likelihood that signature 312 andsignature 332 were created by the same mobile communication unit at thesame time. So, with a high degree of confidence, the locationinformation of signature 332 can be added into signature 312, and/orother parts of signature 312 and signature 332 can be combined, togenerate a useable new reference signature.

By checking one or more of the Power level 1A, Observed cells 1A andTimestamp 1A of signature 332 against signatures in first database 210,it is therefore possible to identify that signature 332 was made by thesame mobile communication unit SU1 as signature 312. In the exampleshown in FIG. 3, dotted line 350 indicates that Observed cells 1A of thesignature 332 are found to match Cell identifier 1 of signature 312.Here a ‘match’ may be an exact correspondence, or a high degree ofcorrelation. Similarly, dotted line 352 indicates that Timestamp 1A ofthe signature 332 is found to match Timestamp 1 of signature 312. In alightly loaded network, for example, the invention may make a matchbetween signatures 332 and 312 using just the timestamp and cell IDinformation. In a more heavily loaded network, the invention may matchthe timestamps, the power levels and the observed cells for multiplecells, in order to match signatures 332 and 312.

In the example shown in FIG. 3, there is more than enough data insignature 332 to link it to signature 312. When such links are alsocreated for other signatures in second database 230 to other signaturesin first database 210, it may be possible to link many or even all ofthe signatures in second database 230 to their corresponding signaturesin first database 210. Thus the invention may lead to a straight-forwardmatching between signatures a location poor, information rich database,such as first database 210, and many or all signatures in a locationrich, information poor database, such as second database 230.

Similar links to those shown in FIG. 3 for signatures 332 and 312 mayalso be found between measurements of parameters in signature 236 fromfirst database 210 and signature 218 from second database 230.

FIG. 4 illustrates an example of the overall result that may beachieved. Signatures 412 and 432 of FIG. 4 correspond to signatures 212and 232 of FIG. 2. Signatures 418 and 436 correspond to signatures 218and 236 of FIG. 2. The remaining reference numbers on FIG. 4 thatcorrespond to those of FIG. 2 indicate similar elements to those in FIG.2.

FIG. 4 shows links made between signatures 412 and 432, and betweensignatures 418 and 436. Reference 460 shows the link between signatures432 and 412. Reference 470 shows the link between signatures 436 and418.

First database 410 also shows an additional signature with reference422. Signature 422 is for mobile communication unit SU3, which wasreferred to in the discussion of FIG. 2. The method may create a link480 between signature 434 in second database 430 and signature 422. Link480 may be based on the correlation between the measurements that makeup signatures 434 and signature 422. Those measurements include RFinformation RF2A within signature 434 and RF information RF2 insignature 422. Signature 434 may comprise measurements of the typesindicated at references 336, 338 and 340 in FIG. 3 for signature 332.Signature 422 may comprise measurements of the types indicated atreferences 316, 318, 320, 322, 324, 326, 328 in FIG. 3 for signature312. Some or all of the measurements that make up signature 434 maymatch exactly or correlate well with the corresponding fields ofsignature 422.

FIG. 5 illustrates in general terms the combining of first database 210,or 410, and second database 230, or 430. This is achieved by linkingmany signatures from database 230, 430 to corresponding signatures indatabase 210, 410. First database 510 is illustrated as being added tosecond database 530 to form a database 580 of reference signatures. Onereference signature 582 is shown in database 580. Reference signature582 is a synthesis of signatures 212 and 232.

Reference signature 582 comprises field 584, which indicates theidentity information of mobile communication unit SU1 from signature212. Field 586 indicates the location ‘LOCI’ from reference signature232. Field 588 generally indicates, as RF1+1A, a synthesis of the othermeasurements from the two signatures 212 and 232. Field 588 may comprisemeasurements derived from all the fields shown as 316, 318, 320, 322,324, 326, 328 and 336, 338 and 340 in FIG. 3. The identity of the mobilecommunication unit may be useful in identifying locations for signaturessuch as 414 and 416 in database 410 of FIG. 4. However, referencesignature 582 may, in an alternative embodiment, be stored in database580 without field 584 indicating the identity of the mobilecommunication unit SU1 from signature 212.

Although the database 580 of reference signatures is shown separatelyfrom both first database 510 and second database 530, this is notnecessarily the case. When location estimates from second database 530,plus other measurement information from signatures in second database530, are added into first database 510, it may be first database 510that eventually stores the reference signatures. This approach mayconvert a pre-existing OSS database into a database of referencesignatures, for example. Alternatively, when data from the signatures infirst database 510 is added into the corresponding signatures in seconddatabase 530, it will be second database 530 that eventually stores thereference signatures.

Due to the nature of RF noise and the random sequencing of independentevents, it is highly improbable that two different mobiles would reportseeing exactly the same cells at exactly the same power levels atexactly the same time. Therefore, this permits unique identification ofa user in first database 510, such as an OSS database, with a very highdegree of confidence, as described above. By extension, the locationfrom the second database 530, such as an anonymised limited RF database,can then be applied to the first database 510, for that user at thatparticular point in time. Other locations associated with any given usercan be similarly applied to the signatures in the first database 510.Hence it is possible to create multiple location estimates for onemobile communication unit SU1, at different times. However, furtherinformation may be derived, as is explained in connection with FIG. 6below.

FIG. 6 illustrates a mobile communication system 600 in accordance withan embodiment of the invention. Mobile communication system 600comprises base station BS1 with reference 602, base station BS2 withreference 604 and base station BS3 with reference 606. Controller 608 islinked to each of the base stations, and may function to implement themethod of the invention. Alternatively, other elements of the mobilecommunication system 600 may implement all or part of the method of theinvention.

The method of FIGS. 2-5 leads to a database 580 with location estimatesfor signatures such as signatures 212 and 218 in FIG. 2. However, firstdatabase 510 also contains other entries, such as signatures 214 and216, which do not contain full RF information, but have only controlinformation. The time stamps of entries in first database 210 show thatsignatures 214 and 216 are ‘intervening events’, since they occurredafter signature 212 but before signature 218. However, the methoddescribed above has provided location estimates for the signatures 212and 218. Each of signatures 214 and 216 can now have a locationassociated with it. This may be achieved either by interpolating betweenthe locations obtained for signatures 212 and 218, or by extrapolatingfrom the location of one of signatures 212 and 218.

FIG. 6 shows four successive locations 612, 614, 616 and 618 for amobile communication unit 620. Mobile communication unit 620 is mobilecommunication unit SU1, which was discussed in connection with FIGS. 2-5above. When mobile communication unit 620 was at location 612, itprovided reference signatures 212 and 232. When mobile communicationunit 620 was at location 618, it provided reference signatures 218 and236. The method described previously has therefore provided locationestimates ‘LOC1’ for location 612 and ‘LOC3’ for location 618.

When mobile communication unit 620 was at location 614, it providedsignature 214. When mobile communication unit 620 was at location 616,it provided signature 216. First database 210 only has controlinformation as part of signatures 214 and 216. However, an estimate oflocations 614 and 616 can still be made, by extrapolating between thelocations LOC1 and LOC3. For example, the total time difference betweenthe timestamps for reference signatures 212 and 218 can be found bysubtraction. Likewise, the spatial separation between locations LOC1 andLOC 3 can be found. Location 614 can then be estimated by dividing upthe spatial separation between locations LOC1 and LOC 3 in the sameproportion as the ratio of (time difference between the timestamp ofreference signatures 212 and 214, divided by the total time differencebetween the timestamps for reference signatures 212 and 218).

In an illustrative numerical example, the time difference between thetimestamps for reference signatures 212 and 218 may be 10 seconds. Thespatial separation between LOC1 and LOC 3 may be 30 meters. If thetimestamp of reference signature 214 is 2 seconds after the timestamp ofreference signature 212, then ⅕^(th) (i.e. 20%) of the total timebetween recording reference signatures 212 and 218 had elapsed whenreference signature 214 was recorded. The distance of 30 meters can bedivided up in a similar ratio. So we can estimate that location 214 is30/5=6 meters from location ‘LOC1’. Without other directionalinformation, we would assume that the location 614 lies in the samedirection from location ‘LOC1’ as does ‘LOC3’.

In a further illustrative numerical example, assume again that the timedifference between the timestamps for reference signatures 212 atlocation 612 and 218 at location 618 is 10 seconds, and the spatialseparation between LOC1 and LOC 3 is 30 meters. If the timestamp ofreference signature 216 at location 616 is 6 seconds after the timestampof reference signature 612, then 6/10ths (i.e. 60%) of the total timebetween reference signatures 212 and 218 had elapsed when referencesignature 216 was recorded. The distance of 30 meters can be divided upin a similar ratio. So we can estimate that location 616 is (30×6)/10=18meters from location ‘LOC1’. Without other directional information, wewould assume that the location 616 lies in the same direction fromlocation ‘LOC1’ as does ‘LOC3’. So location 616 is 18 meters from ‘LOC1’and 12 meters from ‘LOC3’, on a line joining LOC1 and LOC 3.

FIG. 7 illustrates the estimates discussed above in connection with FIG.6. In the embodiment of FIG. 7, first database 210 is illustrated again,as a database with reference 710. However, the reference signaturesderived from signatures 212 and 232 and from 218 and 236 have now beenstored in first database 210, to provide a database 710 of referencesignatures. This is an alternative approach to the creation of database580 in FIG. 5. Signature 712 is a synthesis of signatures 212 and 232,and has location information ‘LOC1’. So reference signature 712comprises similar data to that of reference signature 582 in FIG. 5.Reference signature 718 is a synthesis of reference signatures 218 and236, and has location information ‘LOC3’.

Reference signature 714 is based on reference signature 214. However,the extrapolation approach explained above with reference to FIG. 6 hasled to a location estimate for reference signature 714 of: LOC 1+(x1,y1)

Here x1 is a change in x co-ordinate that represents the displacementalong the x axis of location 614 relative to LOC1. Similarly, y1 is thedisplacement along the y axis of location 614 relative to LOC1. Ifheight data were available, then a further term z1 would indicate anychange in altitude between location 614 and location 612. Analogouslyfor signature 716, x2 and y2 represent the displacements of location 616from LOC1.

FIG. 7 has four reference signatures, each comprising locationinformation. However, the four location estimates all derive from thetwo location estimates ‘LOC1’ and ‘LOC3’, which were part of just thetwo signatures 232 and 236 of FIG. 2. FIG. 7 illustrates howinterpolation or extrapolation of location information may lead to thecreation of more useable reference signatures than there were signaturesin the anonymised database 230.

As has been described above, a location-rich but information-poordatabase can be used in concert with an information-rich butlocation-poor database. The resultant database of reference signaturesmay then aid in geolocating other calls or connections, which do notcomprise location information. Arbitrarily complex reference signaturesmay be generated. These signatures may involve not just Radio Frequency(RF) terms, but other control information terms as well, includingChannel Quality Index (CQI), burst rate, serving cell, etc. This permitsthe construction of reference signatures with location information thatare arbitrarily complex in the following sense:

(i) They combine RF data with non-RF control data such as CQI, burstrate, etc.; and

(ii) They preserve the context of different reference signatures as anaid to geo-location.

This approach also ensures that the constructed reference signaturedatabase 580, 710 is of great relevance, from a user's perspective. Thisis the case, because the reference signature database 580, 710 isconstructed using randomly selected users. Over time, areas within amobile communication system 600 that are more frequented by users willtend to be better represented in the reference signature database. Thisis in contrast to some known drive-test-based strategies, which may beunable to focus on the areas where users are more commonly located.

The advantages of the invention may therefore include some or all of:

(i) Efficient, cost-effective generation of arbitrarily complexreference signatures;

(ii) Ensuring that highly relevant user locations are well-representedin the reference signature database 580, 710;

(iii) Use of the standardized MDT feature from 3GPP, although anysuitably limited location rich database could be used.

(iv) Use of interpolation or extrapolation to provide more referencesignatures with location estimates than there were ‘first’ signatureswith actual location measurement data.

The method can be applied to many cellular telecommunicationstechnologies that provide databases that are location-rich butinformation-poor, as well as databases that are information-rich butlocation-poor. Note-worthy examples are LTE and UMTS.

FIG. 8 summarizes both the creation of the reference signature database580, 710, and its use in a method of geolocation.

In step 810, each signature from second database 230 is correlated orotherwise compared with signatures in first database 210.

In step 820, once a match has been achieved, the location informationfrom each signature in second database 230 is added to the informationfor the corresponding signature in first database 210.

In step 830, location information is estimated for those signatures inthe first database that comprise detail of control events. Thisextrapolation step may, for example, more than double the number ofreference signatures that include a location estimate.

At the end of step 830, a database 580 or 710 of reference signatures isavailable. This database can be used in methods such as that explainedat length in U.S. application Ser. No. 13/369,591.

Step 840 illustrates this use. In step 840, a signature is identifiedthat lacks location information. This ‘unknown’ signature may be arecord of a call reaching first database 210, when first database 210 isthe OSS database of a UMTS mobile communication system. The unknownsignature may be compared to the reference signatures in database 580 or710 of reference signatures. When the RF and other measurements in theunknown signature are close enough to those of one of the referencesignatures in database 580 or 710 of reference signatures, the locationinformation of that reference signature from database 580 or 710 may betaken to be an estimate of the location of the mobile communication unitthat provided the unknown signature.

The ‘unknown’ signature processed in step 840 may be a newly arrivedsignature, which was received after the signatures that make up database580 or 710 of reference signatures. However, the unknown signature mayhave been recorded prior to some of the reference signatures in database580 or 710 of reference signatures. This may be the case, when anattempt is made to geolocate an unknown signature obtained days or evenweeks before the reference signatures in database 580 or 710 werecaptured.

In the foregoing specification, specific embodiments of the presentinvention have been described. However, one of ordinary skill in the artappreciates that various modifications and changes can be made withoutdeparting from the scope of the present invention as set forth in theclaims below. Accordingly, the specification and figures are to beregarded in an illustrative rather than a restrictive sense, and allsuch modifications are intended to be included within the scope ofpresent invention. The benefits, advantages, solutions to problems, andany element(s) that may cause any benefit, advantage, or solution tooccur or become more pronounced are not to be construed as a critical,required, or essential features or elements of any or all the claims.The invention is defined solely by the appended claims including anyamendments made during the pendency of this application and allequivalents of those claims as issued.

What is claimed is:
 1. A method of generating reference signatures foruse in geolocation in a cellular wireless communication system,comprising: obtaining a first signature for a mobile communication unit,the first signature comprising location information, a timestamp, andradio frequency measurement information obtained by the mobilecommunication unit at the location, but not containing identificationinformation for the mobile communication unit; comparing the firstsignature to signatures in a database, to identify a second signature,the second signature having a timestamp and radio frequency measurementinformation that correspond to those of the first signature; andcreating a first reference signature, by combining at least a part ofthe first signature with at least a part of the second signature.
 2. Themethod of claim 1, wherein creating the first reference signaturefurther comprises: combining the location information of the firstsignature with at least a part of the second signature.
 3. The method ofclaim 2, wherein creating the first reference signature furthercomprises: adding the location information of the first signature intothe database holding the second signature.
 4. The method of claim 1,wherein: the second signature comprises a user identifier, and at leastone of the following types of control information not included in thefirst signature: timing advance; burst throughput rate; dynamic ratecontrol, comprising at least channel quality indicators; signal-to-noiseratio.
 5. The method of claim 1, wherein the radio frequency measurementinformation of the first signature comprises at least one selected from:signal quality; and a cell identifier and corresponding observed powerlevel.
 6. The method of claim 1, wherein: the first signature is from ananonymized call, the anonymized call being obtained in accordance withthe Minimization of Drive Test 3GPP standard.
 7. The method of claim 1,further comprising: obtaining a third signature, the third signaturecomprising location information, a timestamp and radio frequencymeasurements obtained at a second location, but not containingidentification information; comparing the third signature to a secondplurality of signatures in the database, to identify a fourth signaturefrom the database having a timestamp and radio frequency measurementinformation that correspond to those of the third signature; and whenthe second and fourth signatures from the database both have theidentification information of the mobile communication unit: creating asecond reference signature, by combining at least a part of the thirdsignature with at least a part of the fourth signature;
 8. The method ofclaim 7, further comprising, when the second and fourth signatures fromthe database both have the identification information of the mobilecommunication unit: creating at least a third reference signature, byinterpolating or extrapolating location information from the firstsignature and the third signature to provide a location estimate for oneor more additional signatures in the database, the one or moreadditional signatures having been obtained for the mobile communicationunit at a time between the timestamp of the second signature and thetimestamp of the fourth signature.
 9. The method of claim 7, whereincreating the second reference signature further comprises: combining thelocation information of the third signature with additional measurementdata associated with the fourth signature.
 10. The method of claim 9,wherein creating the second reference signature further comprises:creating the second reference signature by adding the locationinformation of the third signature into the database holding the fourthsignature.
 11. The method of claim 8, wherein the interpolation oflocation information to create the at least a third reference signaturefurther comprises: deriving a location estimate for each additionalsignature on the basis of: a timestamp of each corresponding additionalsignature in the database; the location information of the firstsignature; and the location information of the third signature.
 12. Themethod of claim 2, wherein: additional measurement data associated withthe second signature comprises: a cell identifier and correspondingobserved power level; and at least one from: signal quality; timingadvance; burst throughput rate; dynamic rate control, comprising atleast channel quality indicators; signal-to-noise ratio; and creatingthe first reference signature comprises combining the locationinformation of the first signature with the additional measurement dataassociated with the second signature.
 13. The method of claim 1, whereincomparing the first signature to the plurality of signatures in thedatabase to identify the second signature further comprises identifyinga second signature that matches the first signature, a second signaturebeing identified as matching the first signature based on: determiningthat the timestamp of the second signature corresponds to the timestampof the first signature, when the timestamp of the second signaturematches the timestamp of the first signature within a predeterminedtiming accuracy; and determining that the radio frequency measurementinformation of the second signature corresponds to the radio frequencymeasurement information of the first signature, when at least a part ofthe radio frequency measurement information of the second signaturematches at least a part of the radio frequency measurement informationof the first signature within a predetermined measurement accuracy. 14.A cellular wireless communication system comprising a database ofreference signatures for use in geolocation, the cellular wirelesscommunication system, operable to: obtain a first signature for a mobilecommunication unit, the first signature comprising location information,a timestamp and radio frequency measurement information obtained by themobile communication unit at the location, but not containingidentification information for the mobile communication unit; comparethe first signature to a plurality of signatures in a database, toidentify a second signature of the plurality of signatures, the secondsignature having a timestamp and radio frequency measurement informationthat correspond to those of the first signature; and create a firstreference signature, by combining at least a part of the first signaturewith at least a part of the second signature.
 15. The cellular wirelesscommunication system of claim 14, further operable to: create the firstreference signature by combining the location information of the firstsignature with at least a part of the second signature.
 16. The cellularwireless communication system of claim 15, further operable to: createthe first reference signature by adding the location information of thefirst signature into the database holding the second signature.
 17. Thecellular wireless communication system of claim 14, further operable to:obtain a third signature, the third signature comprising locationinformation, a timestamp and radio frequency measurements obtained at asecond location, but not containing identification information; comparethe third signature to signatures in the database, to identify a fourthsignature from the database having a timestamp and radio frequencymeasurement information that correspond to those of the third signature;and when the second and fourth signatures from the database both havethe identification information of the mobile communication unit: createa second reference signature, by combining at least a part of the thirdsignature with at least a part of the fourth signature.
 18. The cellularwireless communication system of claim 17, further operable, when thesecond and fourth signatures from the database both have theidentification information of the mobile communication unit, to: createat least a third reference signature, by interpolating or extrapolatinglocation information from the first signature and the third signature toprovide a location estimate for one or more additional signatures in thedatabase, the one or more additional signatures having been obtained forthe mobile communication unit at a time between the timestamp of thesecond signature and the timestamp of the fourth signature.
 19. Thecellular wireless communication system of claim 14, further operable toidentify a second signature that matches the first signature, a secondsignature being identified as matching the first signature based on: thetimestamp of the second signature corresponding to the timestamp of thefirst signature, when the timestamp of the second signature matches thetimestamp of the first signature within a predetermined timing accuracy;and the radio frequency measurement information of the second signaturecorresponding to the radio frequency measurement information of thefirst signature, when at least a part of the radio frequency measurementinformation of the second signature matches at least a part of the radiofrequency measurement information of the first signature within apredetermined measurement accuracy.
 20. A computer-readable storagedevice having executable program code stored therein for programmingsignal processing logic to perform the method of claim 1.